This invention relates to methods and apparatus for processing medical image data to aid in the detection and diagnosis of disease, and more particularly, to methods and apparatus for detecting, quantifying, staging, reporting, and/or tracking of diseases such as chronic obstructive pulmonary disease.
Chronic Obstructive Pulmonary Disease (COPD) is a leading cause of death in the United States and other countries. COPD has two main disease processes, namely, tissue destruction (emphysema) and airway inflammation (chronic bronchitis). At present, there is no known treatment that can reverse the progress of the disease. At best, the progress of the disease can only be halted. Thus, there is a premium placed on early disease diagnosis and treatment. With early diagnosis and effective treatment, a patient's quality of life can be improved.
An x-ray chest radiograph system is the more commonly used diagnostic tool useful for the purpose of detecting lung disease in humans. Lung disease such as bronchitis, emphysema and lung cancer are also detectable in chest radiographs and CT. However, CT systems generally provide over 80 separate images for a single CT scan thereby providing a considerable amount of information to a radiologist for use in interpreting the images and detecting suspect regions that may indicate disease.
Suspect regions are defined as those regions a trained radiologist would recommend following through subsequent diagnostic imaging, biopsy, functional lung testing, or other methods. The considerable volume of data presented by a single CT scan presents a time-consuming process for radiologists. Conventional lung cancer screening generally involves a manual interpretation of the 80 or more images by the radiologist. Fatigue is therefore a significant factor affecting sensitivity and specificity of the human reading. In other diseases, such as emphysema, it is difficult for a radiologist to classify the extent of disease progression by only looking at the CT images.
COPD is identified based on symptoms including coughing, wheezing, and shortness of breath (dyspnea). COPD includes a number of respiratory diseases, the most prominent of which are emphysema and chronic bronchitis. COPD affects large airways, small airways and parenchyma in patients. Diseases are typically caused by smoking and air pollution, and are linked to genetic predisposition causing alpha-anti-elastase deficiency.
Emphysema, or airspace destruction, is the most prominent feature of parenchymal change in COPD patients. Emphysema is the result of the loss of elastic recoil of lung tissue. There are four types of emphysema: centrilobular, panlobular or panacinar, distal acinar or paraseptal, and irregular. The first two types contribute to the majority of emphysematous COPD. The classification is based on the anatomical distribution of airspace destruction within a lobule, which is a cluster of acini. Currently, emphysema can be classified only through post mortem examination. Emphysema is typically diagnosed by gross physiological responses, medical imaging and post mortem anatomical inspection. The use of high resolution CT image data is a promising technique for measuring the lung volume for diagnosis purposes. However, one of the more prominent disease indicators is degradation of the alveoli and other tissue changes of the lung which are currently difficult to measure from CT image data.
Detecting emphysema at early stages is most desirable. The damage caused by emphysema is often detected at later stages of the disease and the effects are permanent. Although the effects of emphysema cannot be reversed, early diagnosis of emphysema may enable measures to be taken by the patient to prevent further progression of the damage caused by the disease. Further, as more and more therapy and drug treatments are discovered, it will be desirable to monitor a patient's response to such treatment.
Chronic bronchitis causes anatomical airway narrowing, which reduces lung function. Airway modification typically begins with irritation from smoking and/or air pollution and can be caused/exacerbated by biological infection. Chronic bronchitis is clinically defined by persistent cough and sputum production for more than 3 months in a 2-year period. Chronic bronchitis can be classified into simple chronic bronchitis, obstructive bronchitis and chronic asthmatic bronchitis. In simple chronic bronchitis, no sputum is produced. Chronic asthmatic bronchitis involves hyperreactivity of the airways. In obstructive chronic bronchitis, airflow is hindered by airway modification. Chronic bronchitis is currently staged using Reid index post mortem. High resolution CT may enable scoring chronic bronchitis using Reid index in vivo.
Bronchial wall cross-sectional area is a key indicator in the diagnosis and staging of COPD. Measuring airway cross-sectional area from medical images (for instance CT) will enable physicians to track disease progression and accelerate clinical trials. Bronchial passages appear in CT images as small dark regions surrounded by bright regions. The dark area is the lumen while the bright area is composed of both the bronchial wall and any attaching or adjacent blood vessels. In measuring the airway wall cross-sectional area, one must not incorporate the thickness of the attaching or adjacent blood vessels.
If the airway is isolated, with no attaching or adjacent blood vessels, the airway can be measured using a variety of standard image processing and computer vision techniques. When the imaged airway has attached of adjacent blood vessels, an example of traditional approach has been to manually select a ray from the center of the lumen that passes through the airway wall at a point where the are no blood vessels. The measure of the wall thickness along this single ray is used to estimate the airway cross-sectional area.
Some known diagnosis techniques have attempted to use simple Computed Tomographic (CT) images to attempt to quantify emphysema. However, known techniques are not based on an underlying model of the disease, and the reliability of the results obtained with these techniques can be affected by variable scan parameters and scanner calibration as well as other disease pathologies. In addition, known techniques do not provide estimates of the rate or location of tissue destruction.